Experimental characterization of fluid and squeeze film effects in heat exchanger tube supports

Abstract

The fluid and squeeze film characteristics inside cylindrical heat exchanger tube support holes and at anti-vibration bar (AVB) supports were determined experimentally. A rigid tube was oscillated inside a specially instrumented tube support housing. This allowed direct measurement of the localized force exchange between tube and support as a function of the instantaneous tube motion parameters (acceleration, velocity and tube-to-support gap). Tests were conducted with and without the tube impacting against the support simulant. Different tube support geometries (clearance and height) and surface roughnesses were investigated. One geometry was tested over a wide range of fluid viscosities and with the tube canted at different angles relative to the support axis. Semi-empirical equations of the fluid and squeeze film reaction forces were generated. These expressions were developed using an extensive experimental database. For smooth cylindrical supports the fluid/squeeze film effects were represented by separate correlations for three different crevice gap ranges. The relatively simple fluid film effects, which prevail for gaps larger than a few mils (1 mil ≅ 25 μm), are governed by mass- and damping-proportional terms. For smaller gaps, squeeze film phenomena occur which, in addition to the mass term, are controlled by instantaneous crevice gap and tube velocity values. Two sets of semi-empirical expressions were sufficient to model the squeeze film effects.